Heat-sensitive recording materials on paper webs have been known for many years and are steadily gaining in popularity. This may be explained by the fact that their use as tickets in particular offers great advantages to ticket suppliers. Because the color-forming components in the heat-sensitive recording process reside in the recording material itself, it is possible to employ large numbers of printers which operate without toner or ink cartridges and whose function need no longer be monitored by persons at regular intervals. Accordingly, this innovative technology has had extensive success particularly in public transportation, busses and rail transportation, air travel, stadium and museum ticket kiosks, and parking receipt dispensers.
There have been numerous attempts to improve the known heat-sensitive recording materials, particularly for economizing on resources for environmental reasons. One such attempt consists in the use of recycled fibers in the paper web substrate for the recording layer. For example, DE-C-40 37 299 discloses the fundamental suggestion to use a coating base paper whose fiber content is made up of at least 95 percent by weight of recovered paper. However, this reference does not address the problems arising from the use of recovered paper with regard to background darkening and resistance over time of print images formed by the supply of heat.
To remedy the problems left unsolved by DE-C-40 37 299, it is proposed in EP-B-1 413 452 to use 4-hydroxybenzenesulfone anilide as acceptor in the heat-sensitive recording layer. Without doubt, this reference represents a great improvement in the use of paper webs with recycled fibers because it was able to overcome the considerable disadvantages arising from the low stability of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), which is explicitly mentioned therein, as an acceptor in heat-sensitive recording layers.
With knowledge of the prior art referenced herein, it was an object of the invention to provide a substantial improvement in an alternative heat-sensitive recording material with a paper web having recycled fibers with respect to the resistance of print images formed by the supply of heat relative to oils, plasticizers, as well as heat. It is precisely these resistances which are particularly important for the intended use of the heat-sensitive recording material suggested herein as tickets. Another important focus is the whiteness of the recording layer because a gray recording layer causes errors in character recognition; further, grayish recording materials used as tickets are not deemed acceptable commercially.